Vacuum IG window unit with edge seal at least partially diffused at temper and completed via microwave curing, and corresponding method of making the same

ABSTRACT

A vacuum insulating glass (IG) unit and method of manufacturing the same. A peripheral or edge seal ( 11 ) of a vacuum IG unit is formed utilizing microwave energy ( 17 ) in order to enable tempered glass sheets ( 2, 3 ) of the IG unit to retain a significant portion of their original temper strength. In certain exemplary embodiments, the edge seal may be formed of glass frit or solder glass. In certain embodiments, at least a portion ( 12, 12   a   , 301 ) of the edge seal material may be deposited on one or both substrates prior to a thermal tempering process so that during tempering the edge seal material is permitted to diffuse into (i.e., bond to) the glass substrate(s) ( 2, 3 ). Optionally, additional edge seal material ( 303 ) may be added after tempering. The final edge seal ( 11 ) is preferably formed via microwave heating ( 17 ) of the edge seal material.

[0001] This application is a continuation-in-part (CIP) application ofeach of U.S. Ser. No. 09/722,008, filed Nov. 27, 2000 (attorneyreference number 3691-103), and Ser. No. 09/670,559, filed Sep. 27, 2000(attorney reference number 3691-89), the disclosures of which are allhereby incorporated herein by reference.

RELATED APPLICATIONS

[0002] This application is related to commonly owned U.S. Ser. Nos.09/303,550, 09/722,008, 09/348,281, 09/670,559, and 09/404,659, all ofwhich are hereby incorporated herein by reference.

[0003] This invention relates to a vacuum insulating glass (IG) unit,and a method of making the same.

BACKGROUND OF THE INVENTION

[0004] Vacuum IG units are known in the art. For example, see U.S. Pat.Nos. 5,664,395, 5,657,607, and 5,902,652, the disclosures of which areall hereby incorporated herein by reference.

[0005] Prior art FIGS. 1-2 illustrate a conventional vacuum IG unit. IGunit 1 includes two spaced apart glass substrates 2 and 3 which enclosean evacuated or low pressure space 6 therebetween. Glasssheets/substrates 2 and 3 are interconnected by peripheral or edge sealof fused solder glass 4 and an array of support pillars or spacers 5.

[0006] Pump out tube 8 is hermetically sealed by solder glass 9 to anaperture or hole 10 which passes from an interior surface of glass sheet2 to the bottom of recess 11 in the exterior face of sheet 2. A vacuumis attached to pump out tube 8 so that the interior cavity betweensubstrates 2 and 3 can be evacuated to create a low pressure area orspace 6. After evacuation, tube 8 is melted to seal the vacuum. Recess11 retains sealed tube 8. Optionally, a chemical getter 12 may beincluded within recess 13.

[0007] Conventional vacuum IG units, with their fused solder glassperipheral seals 4, have been manufactured as follows. Glass frit in asolution (ultimately to form solder glass edge seal 4) is initiallydeposited around the periphery of substrate 2. The other substrate 3 isbrought down over top of substrate 2 so as to sandwich spacers 5 and theglass frit/solution therebetween. The entire assembly including sheets2, 3, the spacers, and the seal material is then heated to a temperatureof approximately 500° C. at which point the glass frit melts, wets thesurfaces of the glass sheets 2, 3, and ultimately forms hermeticperipheral or edge seal 4. This approximately 500° C. temperature ismaintained for from about one to eight hours. After formation of theperipheral/edge seal 4 and the seal around tube 8, the assembly iscooled to room temperature. It is noted that column 2 of U.S. Pat. No.5,664,395 states that a conventional vacuum IG processing temperature isapproximately 500° C. for one hour. Inventor Collins of the '395 patentstates in “Thermal Outgassing of Vacuum Glazing”, by Lenzen, Turner andCollins, that “the edge seal process is currently quite slow: typicallythe temperature of the sample is increased at 200° C. per hour, and heldfor one hour at a constant value ranging from 430° C. and 530° C.depending on the solder glass composition.” After formation of edge seal4, a vacuum is drawn via the tube to form low pressure space 6.

[0008] Unfortunately, the aforesaid high temperatures and long heatingtimes utilized in the formulation of edge seal 4 are undesirable,especially when it is desired to use a tempered glass substrate(s) 2, 3in the vacuum IG unit. As shown in FIGS. 3-4, tempered glass losestemper strength upon exposure to high temperatures as a function ofheating time. Moreover, such high processing temperatures may adverselyaffect certain low-E coating(s) that may be applied to one or both ofthe glass substrates.

[0009]FIG. 3 is a graph illustrating how fully thermally tempered plateglass loses original temper upon exposure to different temperatures fordifferent periods of time, where the original center tension stress is3,200 MU per inch. The x-axis in FIG. 3 is exponentially representativeof time in hours (from 1 to 1,000 hours), while the y-axis is indicativeof the percentage of original temper strength remaining after heatexposure. FIG. 4 is a graph similar to FIG. 3, except that the x-axis inFIG. 4 extends from zero to one hour exponentially.

[0010] Seven different curves are illustrated in FIG. 3, each indicativeof a different temperature exposure in degrees Fahrenheit (F.). Thedifferent curves/lines are 400° F. (across the top of the FIG. 3 graph),500° F., 600° F., 700° F., 800° F., 900° F., and 950° F. (the bottomcurve of the FIG. 3 graph). A temperature of 900° F. is equivalent toapproximately 482° C., which is within the range utilized for formingthe aforesaid conventional solder glass peripheral seal 4 in FIGS. 1-2.Thus, attention is drawn to the 900° F. curve in FIG. 3, labeled byreference number 18. As shown, only 20% of the original temper strengthremains after one hour at this temperature (900° F. or 482° C.). Such asignificant loss (i.e., 80% loss) of temper strength is of courseundesirable.

[0011] In FIGS. 3-4, it is noted that much better temper strengthremains in a thermally tempered sheet when it is heated to a temperatureof 800° F. (i.e., about 428° C.) for one hour as opposed to 900° F. forone hour. Such a glass sheet retains about 70% of its original temperstrength after one hour at 800° F., which is significantly better thanthe less than 20% when at 900° F. for the same period of time.

[0012] Another advantage associated with not heating up the entire unitfor too long is that lower temperature pillar materials may then beused. This may or may not be desirable in some instances.

[0013] It will be apparent of those of skill in the art that thereexists a need for a vacuum IG unit, and corresponding method of makingthe same, where a structurally sound hermetic edge seal may be providedbetween opposing glass sheets without at least certain portions ofthermally tempered glass sheet(s)/substrate(s) of the IG unit losingmore than about 50% of original temper strength. There also exists aneed in the art for a vacuum IG unit including tempered glass sheets,wherein the peripheral seal is formed such that the glass sheets retainmore of their original temper strength than with a conventional vacuumIG manufacturing technique where the entire unit is heated in order toform a solder glass edge seal. It is a purpose of this invention tofulfill one or more of the above listed needs in the art.

SUMMARY OF THE INVENTION

[0014] An object of this invention is to provide a vacuum IG unit havinga peripheral or edge seal formed so that at least certain portion(s) ofthermally tempered glass substrates/sheets of the IG unit retain more oftheir original temper strength than if conventional edge seal formingtechniques were used with the solder glass edge seal material.

[0015] Another object of this invention is to provide a vacuum IG unit,and method of making the same, wherein at least a portion of theresulting thermally tempered glass substrate(s) retain(s) at least about50% of original temper strength after formation of the edge seal (e.g.,solder glass edge seal).

[0016] Another object of this invention is to reduce the amount ofpost-tempering heating time necessary to form a peripheral/edge seal ina vacuum IG unit.

[0017] Yet another object of this invention is to form a hermetic edgeseal in a vacuum IG unit by utilizing microwave energy to cure edge sealmaterial. In an exemplary embodiment, glass frit suspended in liquid orsolution may be deposited as an edge seal base material on each of firstand second annealed glass substrates (e.g., soda-lime-silica float glasssubstrates). This may be referred to as an initial or first glass fritapplication. Each of the glass substrates may then be thermally temperedwith the edge seal material thereon so that during the thermal temperingprocess, the edge seal material at least partially diffuses into and/orbonds to the respective glass substrates. This fuses the glass frit edgeseal material to the glass substrates (i.e., pre-firing the first glassfrit application) while at the same time tempering the substrates.Thereafter, a second application of glass frit may be applied to one orboth of the substrates over the pre-fired first glass frit application.Spacers and/or pillars may be sandwiched between the substrates as thesubstrates are brought together. Then, microwave energy is directedtoward the edge seal material in order to heat the same (i.e., heatingat least the second glass frit application, and preferably both thefirst and second glass frit applications) thereby causing the secondglass frit edge seal material to fuse to, or bond with, the first orpre-fired glass frit base material on both substrates thereby creating ahermetic edge seal.

[0018] In certain embodiments, the first application of glass frit edgeseal material is deposited on the respective substrates prior to thermaltempering, because diffusion of solder glass or glass frit into anannealed non-tempered glass substrate may be easier than diffusion ofsolder glass or glass frit into a tempered glass substrate. Thus, bycausing the edge seal material to fuse into the glass substrate(s)during the tempering process yet prior to full tempering of thesubstrate(s), a better bond of the edge seal to the substrate(s) may beachieved.

[0019] Moreover, the use of microwave energy (localized or otherwise) inorder to form an edge seal (e.g., using the second glass fritapplication) enables one or both of the thermally tempered glasssheets/substrates to retain much temper strength because at leastcertain portions (e.g., central portions) of the glass substrate(s) neednot be heated along with the solder glass edge seal material duringformation of the edge seal. Moreover, the use of microwave energy informing the edge seal of a vacuum IG unit can result in reducedprocessing time as well as a reduced need for capital intensivemanufacturing equipment such as ovens, furnaces, or the like.

[0020] Another object of this invention is to fulfill one or more of theabove listed objects and/or needs.

[0021] Generally speaking, certain embodiments of this invention fulfillone or more of the above-listed needs and/or objects by providing amethod of making a thermally insulating unit, the method comprising:

[0022] providing first and second substrates with a plurality of spacerstherebetween; and

[0023] forming a hermetic peripheral or edge seal at least partiallybetween the first and second substrates using at least microwave energy.

[0024] Certain embodiments of this invention further fulfill one or moreof the above-listed needs by providing a method of making a thermallyinsulating glass panel, the method comprising:

[0025] depositing a first portion of edge seal material on first andsecond glass substrates;

[0026] thermally tempering the first and second glass substrates withthe first portion of edge seal material thereon;

[0027] following said tempering, depositing a second portion of edgeseal material on at least the first substrate over at least part of thefirst portion of edge seal material already on the first substrate;

[0028] forming a hermetic peripheral or edge seal at least partiallybetween the first and second substrates by at least using microwaveenergy directed toward at least the second portion of edge seal materialso that the second portion of edge seal material bonds to both: a) thefirst portion of edge seal material on the first substrate, and b) thefirst portion of edge seal material on the second substrate; and

[0029] evacuating a space between the first and second substrates so asto form a low pressure area having a pressure less than atmosphericpressure between the first and second substrates.

[0030] Certain other embodiments of this invention fulfill one or moreof the above-listed needs by providing a thermally insulating panelcomprising:

[0031] first and second spaced apart substrates having a low pressurespace therebetween having a pressure less than atmospheric pressure;

[0032] a hermetic seal provided between said first and secondsubstrates; and

[0033] wherein said seal includes first and second solder glass or glassfrit seal portions, at least a portion of said first seal portion havingbeen deposited on said first substrate prior to tempering thereof andsaid second seal portion having been deposited on one of said substratesfollowing tempering thereof.

IN THE DRAWINGS

[0034]FIG. 1 is a prior art cross-sectional view of a conventionalvacuum IG unit.

[0035]FIG. 2 is a prior art top plan view of the bottom substrate, edgeseal, and spacers of the FIG. 1 vacuum IG unit taken along the sectionline illustrated in FIG. 1.

[0036]FIG. 3 is a graph correlating time (hours) versus percenttempering strength remaining, illustrating the loss of original temperstrength for a thermally tempered sheet of glass after exposure todifferent temperatures for different periods of time.

[0037]FIG. 4 is a graph correlating time versus percent temperingstrength remaining similar to that of FIG. 3 except that a smaller timeperiod is provided on the x-axis.

[0038]FIG. 5 is a side cross-sectional view of a vacuum IG unitaccording to an embodiment of this invention.

[0039] FIGS. 6(a) through 6(c) illustrate certain manufacturing stepsperformed during the manufacture of the vacuum IG unit of FIG. 5according to an embodiment of this invention.

[0040]FIG. 7 is a flow chart illustrating certain steps performedaccording to an embodiment of this invention in forming a vacuum IGwindow unit.

[0041]FIG. 8 is a cross sectional view of a portion of a vacuum IGwindow unit illustrating that a seal around a pump-out tube may beformed using microwave energy according to an embodiment of thisinvention.

[0042]FIG. 9 is a flowchart illustrating certain steps taken inaccordance with yet another embodiment of this invention.

[0043] FIGS. 10(a) through 10(c) are side partial cross sectional viewof one or two glass substrates of at least a portion of a VIG unitduring the manufacture of the same according to another embodiment ofthis invention.

[0044]FIG. 11 is a flowchart illustrating certain steps taken during themanufacture of the VIG unit according to the FIG. 10 embodiment of thisinvention.

[0045]FIG. 12 is a flowchart illustrating certain steps taken during themanufacture of a VIG unit according to still another embodiment of thisinvention.

[0046] FIGS. 13(a) through 13(c) are side partial cross sectional viewsof components as the VIG unit is being manufactured in accordance withthe FIG. 12 embodiment of this invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THIS INVENTION

[0047] Referring now more particularly to the accompanying drawings inwhich like reference numerals indicate like parts throughout the severalviews.

[0048] Certain embodiments of this invention relate to an improvedperipheral or edge seal in a vacuum IG window unit, and/or a method ofmaking the same. “Peripheral” and “edge” seals herein do not mean thatthe seals are located at the absolute periphery or edge of the unit, butinstead mean that the seal is at least partially located at or near(e.g., within about two inches) an edge of at least one substrate of theunit.

[0049] Certain embodiments of this invention utilize microwave energyduring the formation of an edge or other seal for a vacuum IG unit. Inan exemplary embodiment, microwave energy may be used in order to cureedge seal material into a resulting edge seal (e.g., solder glassinclusive edge seal) in a vacuum IG unit. As will be explained morefully below, the use of microwave energy may enable at least portion(s)of one or more of the thermally tempered glass substrate(s) 2, 3 toretain more temper strength than they otherwise would during aconventional formation of a solder glass edge seal in a vacuum IG unit.Additionally, the use of microwave energy may reduce the likelihood ofdamage to an optional low-E coating(s) provided on one or more of theglass substrates. Still further, the use of microwave energy duringformation of a solder glass edge seal may enable processing time to bereduced relative to conventional solder glass edge seal curing times.Thus, while tempered substrates 2, 3 are preferred, they are notnecessary and non-tempered substrates 2, 3 may instead be used incertain alternative embodiments of this invention.

[0050] FIGS. 5, 6(c), 10(c), and 13(c) are cross-sectional views ofthermally insulating glass panels according to different embodiments ofthis invention. Because interior space or cavity 6 between the opposingsubstrates is at a pressure lower than atmospheric in general, this typeof panel is often referred to as a vacuum insulating glass (IG) unithaving low pressure space 6. The vacuum IG unit or panel includes firstglass substrate 2, second glass substrate 3, low pressure or evacuatedspace 6 provided between substrates 2 and 3, spacers/pillars 5 forspacing the substrates 2, 3 from one another and supporting them,optional pump out tube (not shown) disposed in a hole or aperture formedin one of the substrates for evacuating space 6, and peripheral or edgeseal 11 that hermetically seals low pressure space 6 between substrates2, 3. Hermetic edge seal 11 prevents air from entering space 6 and keepsthe vacuum therein. Seal 11 in certain embodiments of this invention maybe located in approximately the same location as edge seal 4 shown inFIG. 2. Any other suitable location is possible so long as a lowpressure space 6 is sealed off between the substrates. Substrates 2, 3are preferably thermally tempered glass, although they need not betempered in all embodiments of this invention.

[0051] In certain embodiments of this invention, glass substrates 2, 3may be approximately the same size. However, in other embodiments ofthis invention, one glass substrate 2 may be larger in size than theother glass substrate 3 in order to provide an approximately L-shapedstep proximate an edge of the vacuum IG unit.

[0052] Vacuum IG units according to different embodiments of thisinvention may be used as residential or commercial windows. Theevacuation of space 6 eliminates or reduces heat transport between glasssubstrates 2, 3 due to gaseous conduction and convection. In addition,radiative heat transport between glass sheets/substrates 2 and 3 can bereduced to a low level by providing an optional low emissivity (low-E)coating(s) on the internal surface of one or both substrates 2, 3. Suchlow-E coating(s) are typically edge deleted under edge seals, but neednot be in certain embodiments of this invention. High levels of thermalinsulation can thus be achieved. In certain embodiments, the pressure inspace 6 is reduced to a level below about 10⁻² Torr, more preferablybelow about 1.0 mTorr, or 10⁻³ Torr, and most preferably below about10⁻⁴ Torr of atmospheric pressure. To maintain such pressures, theinternal surfaces of glass substrates 2, 3 may be outgassed, and areasat or near the edges or peripheries of substrates 2, 3 hermeticallysealed together by seal 11 in order to eliminate any ingress of gas orair.

[0053] As shown in FIGS. 5, 6(c), 10(c), and 13(c), an array of small,high strength support spacers or pillars 5 is provided betweensubstrates 2 and 3 in order to maintain separation of the approximatelyparallel glass substrates against atmospheric pressure. It is oftendesirable for spacers 5 to be sufficiently small so that they arevisibly unobtrusive. In certain embodiments, each pillar or spacer 5 mayhave a height of from about 0.20 to 1.0 mm, more preferably from about0.20 to 0.40 mm. Spacers 5 may be made of solder glass, ceramic, metal,or any other suitable material in different embodiments of thisinvention. The may be dime-shaped, cylindrical in shape, round, or anyother suitable shape in different embodiments of this invention.

[0054] Tempered glass sheets 2 and 3 are preferred for their mechanicaland thermal strength. Tempered glass has been used traditionally incommercial applications where wind, snow or thermal loads exceed thestrength capabilities of other glass and/or where tempered glass ismandated by code (e.g., safety glazings for entranceways, railings, orfire knock-out windows). In certain preferred embodiments of thisinvention, glass substrates 2 and/or 3 are thermally or heat tempered.By providing tempered glass substrates 2 and 3, the strength of theglass is increased. This may enable pillars to be spaced further apart,which increases stresses at the glass/pillar interface(s) but maypotentially result in less pillars being utilized in the vacuum IG unit.Reduction in a number of pillars may enhance the thermal insulationproperties of the vacuum IG unit and/or improve aestheticcharacteristics of the unit. In preferred embodiments of this invention,the glass sheets 2, 3 are thermally tempered prior to their sandwichingof the spacers 5 therebetween.

[0055] According to certain embodiments of this invention, the glassused for substrates 2 and 3 is soda lime silica glass. However, othertypes of glass, colored or clear, may also be used (e.g., borosilicateglass). Glass substrates 2 and/or 3 may be from about 2 to 6 mm thick incertain embodiments, preferably from about 3-5 mm thick each. However,when tempered, thinner glass sheets 2, 3 may be used (e.g., from about2.5 to 4.0 mm thick). It is also possible to use plastic substrates 2, 3in alternative embodiments of this invention.

[0056] According to preferred embodiments of this invention, solderglass edge seal 11 is formed at a location at least partially betweensubstrates 2 and 3 through the use of at least microwave energy. Themicrowave energy is directed toward the edge seal material in order tocure the same into the resulting solder glass edge seal 11. In certainembodiments of this invention, the microwave energy may be directedtoward localized areas of the vacuum IG unit where the edge seal is tobe formed in order to avoid substantially heating central areas of theglass substrates 2, 3 so that at least certain portions (e.g., centralportions) of the glass substrates can retain much of their originaltemper strength. In other embodiments of this invention, microwaveenergy sensitive additives or dopants may be provided in the edge sealmaterial so that the edge seal material absorbs more microwave energythan do glass sheets 2, 3. Again, it is possible to heat the edge sealmaterial and form hermetic solder edge seal 11 while at the same timeenabling large portions of glass sheets 2, 3 (and potentially the entiresubstrates 2, 3) to retain much of their original temper strength.

[0057] FIGS. 6(a)-6(c) are side cross-sectional views illustrating stepstaken during the manufacture of an exemplary vacuum IG unit according toa particular embodiment of this invention. Initially, first and secondglass substrates 2, 3 are provided. At least one of the substrates ispreferably thermally tempered, and both may be tempered in certainembodiments. As shown in FIG. 6(a), a plurality of spacers 5 and edgeseal material 12 are deposited on a major surface of tempered glasssubstrate 2. Spacers 5 may be deposited before edge seal material 12, orvice versa.

[0058] According to an exemplary embodiment, glass frit suspended in aliquid or solvent is deposited around an edge of substrate 2 as edgeseal material 12. The frit is known in the art as a particulate-likesubstance (e.g., pulverized, ground, or and/powdered glass). Anexemplary solvent in which the glass frit may be suspended in edge sealmaterial 12 is amyl acetate. Optionally, a binder such as methylcellulose or nitrocellulose may be added to the solvent. Thus, accordingto one exemplary embodiment, the solder glass or edge seal material 12deposited proximate the periphery of the major interior surface ofsubstrate 2 may include about 90% glass frit powder, and 10% solution.In certain embodiments, material 12 may include from about 70-99% glassfrit powder, and from about 1-30% solution. The solution may include,for example, 98.8% amyl acetate and 1.2% nitrocellulose (by weight).Other suitable solutions and/or ratios may of course be utilizedinstead, as the aforesaid materials and ratios are for purposes ofexample only. For example, frit powder Ferro 4000 (from Ferro Corp.,Cleveland, Ohio) and binder/solvent F1016AJ (e.g., mixture of 85% Ferro4000 and 15% by weight F1016AJ) may be used for the edge seal materialto be deposited, and the same may be deposited on one of substrates 2, 3via a syringe or any other suitable dispenser.

[0059] After the spacers 5 and edge seal material 12 have been providedon the surface of substrate 2, the other substrate 3 is brought down ontop of spacers 5 and edge seal material 12 as shown in FIG. 6(b). Atthis point, primarily spacers 5 function to support substrate 3 abovesubstrate 2. Optionally, a low-E coating or coating system 14 may beprovided on an interior surface of substrate 3. Exemplary low-E coatingsystems 14 which may be used are disclosed in U.S. Pat. Nos. 5,557,462,5,514,476, 5,425,861, and 5,800,933, the disclosures of which are allhereby incorporated herein by reference.

[0060] As shown in FIG. 6(c), microwave energy 17 is then directedtoward the edge seal material 12 (e.g., through substrate 2 and/or 3) inorder to heat and cure the same in order to form the resulting hermeticperipheral/edge seal 11. In this regard, the glass frit in edge sealmaterial 12 is heated, melted and/or fused by the microwave energy whichit absorbs and the solvent is driven off in order to formperipheral/edge seal 11 of solder glass which bonds to substrates 2, 3.Optionally, at least one dopant material(s) may be added to the edgeseal material 12 in order to render the edge seal material moreabsorptive of the microwave energy (e.g., more absorptive of themicrowave energy than the substrates 2, 3). For example, a dopant suchas silicon carbide may be added to the edge seal material 12 in order toincrease its microwave absorption relative to that of glass sheets 2, 3.While silicon carbide is a preferred dopant for increasing the microwaveabsorption of seal material 12, other suitable dopants (e.g., metalssuch as Al, Cu, Mg, alloys thereof, etc.) may instead be added to edgeseal material 12 to increase its microwave absorption. In certainpreferred embodiments, the dopant may represent from about 0-15% byweight of the edge seal material, more preferably from about 2-10%, andmost preferably from about 5-8%.

[0061] As shown in FIG. 6(c), a localized beam 17 of microwave energyfrom microwave generator 15 may be directed only toward the area of thevacuum IG unit where hermetic peripheral/edge seal 11 is to be formed.In other words, microwave energy need not be directed toward a centralarea of the vacuum IG unit near the center or primary viewing area(s) ofglass sheets 2, 3. In such a manner, microwave heating of the centralportions of the vacuum IG unit can be avoided so that at least centralportions of glass substrates 2, 3 can retain at least about 50% (andpreferably more) of their original temper strength after the edge seal11 has been formed. Microwave generator 15 may be robotically controlledto traverse the entire periphery and/or edge of the vacuum IG unit whiledirecting beam 17 only at the area along the edge of the unit where seal11 is to be formed thereby avoiding the direction of microwave energytoward and/or into central portions of the substrates 2, 3. Beam 17 maybe in the form of a point-shaped beam for directing energy only at aspecific point of the unit, or alternatively the beam 17 may be alinearly shaped beam so as to direct microwave energy at an area shapedin a linear and elongated manner (e.g., along a partial or entire edgeof the unit).

[0062] Alternatively, instead of directing the microwave energy towardthe vacuum IG unit in the form of a beam 17, the entire vacuum IG unitincluding the entireties of both substrates 2, 3, and seal material 12may be passed through a microwave oven for the purpose of heating andforming hermetic edge seal 11. In such embodiments (and all otherembodiments herein), at least one dopant (e.g., silicon carbide) may beadded to the edge seal material 12 so as to render it more absorbing ofmicrowave energy than glass substrates 2, 3. In such a manner, while theedge seal material 12 absorbs much microwave energy and fuses so as toform hermetic solder glass edge seal 11, substrates 2 and 3 do notabsorb nearly as much microwave energy and are not heated as much as theedge seal material. This, for example, enables the substrates to becapable of retaining at least 50% (and preferably more) of theiroriginal temper strength. In still other embodiments of this invention,substantially the entire unit may be flooded with microwave energy (withuse of a dopant in the edge seal material) for a period of about 10seconds or less, in which case most of the thermal temper strength canbe retained even after such microwaving.

[0063] While fused solder glass is a preferred material of edge seal 11according to certain embodiments of this invention, other materialscapable of forming a hermetic edge seal may instead be used. Forexample, hermetic edge seal 11 may be formed of indium, epoxy, or othersuitable material in alternative embodiments of this invention (thesematerials also being exposed to the microwave energy in order to curethe same to form seal 11).

[0064] In preferred embodiments of this invention, the microwave energy17 utilized to form hermetic edge seal 11 has a wavelength of from about1 -10 mm, more preferably from about 2-8 mm, and most preferably fromabout 2-5 mm. Wavelengths much higher than these are not easily absorbedby glass but could be utilized if sufficient dopant was provided in theedge seal material 12. Thus, while the aforesaid microwave wavelengthsare preferred, they are not intended to be limiting unless specificallyrecited in the claims.

[0065] In an exemplary embodiment of this invention, microwave generator15 may be a Gyrotron Beam Generator which may be obtained by GyrotronTechnologies, Inc., Bristol, Pa. However, as will be recognized by thoseof skill in the art, other suitable microwave generators may instead byused (e.g., directional beam microwave generators, oven type microwavegenerators, etc.).

[0066] As discussed above, a primary purpose of certain embodiments ofthis invention is to utilize microwave energy 17 which (i) heats edgeseal material 12 in order to form hermetic peripheral/edge seal 11,while (ii) not substantially heating certain portions (e.g., centralportions) of the glass substrate(s) 2, 3 so as to not adversely affectthe temper strength of substrates 2 and 3 to any significant degree.Thus, at least certain portions of substrates 2 and 3 (and potentiallythe entire substrates) preferably retain at least about 50% of theiroriginal temper strength after hermetic edge seal 11 has been formed,more preferably at least about 60% of their original temper strength,even more preferably at least about 70% of their original temperstrength, and most preferably at least about 80% of their originaltemper strength. This may be achieved by directing the microwave energy17 in a localized manner only at the area (e.g., near a periphery) ofthe vacuum IG unit where the edge seal 11 is to be formed so as toprevent or reduce the likelihood of central portions of glass substrates2, 3 absorbing significant microwave energy. Alternatively, this may beachieved by using an edge seal material 12 (e.g., glass frit in asolvent with dopant) which tends to absorb significantly more microwaveenergy than do substrates 2, 3. In any event, hermetic edge seal 11 isformed without significant deterioration of the temper strength of atleast certain portions (e.g., central portions) of the glass substrates2, 3.

[0067] In certain embodiments of this invention, each area of edge sealmaterial 12 is heated with microwave energy for a limited period of timein order to form hermetic seal 11. For example, in one embodiment eacharea of edge seal material 12 may be heated with microwave energy for atime of from about 1-60 seconds, more preferably from about 1-30seconds. However, depending upon the edge seal material being used, theexposure time may vary and may last for minutes in other embodiments.However, it is noted that when appropriate edge seal materials areutilized, the processing time for forming hermetic edge seal 11 can bereduced relative to that of the prior art.

[0068]FIG. 7 is a flow chart illustrating certain steps taken in themanufacture of a vacuum IG unit of FIGS. 5-6 according to an exemplaryembodiment of this invention. Initially, the glass substrates 2, 3 areprovided (step 21). The glass substrates 2, 3 are preferably thermallytempered (step 23). Optionally, a low-E coating or coating system 14 maybe provided on at least one of the substrates 2, 3 (step 25), eitherbefore tempering or after tempering in different embodiments. Spacers 5and edge seal material 12 (e.g., glass frit suspended in liquid orsolvent) is deposited around an edge or periphery of a major surface ofthe first substrate 2 (step 27) (e.g., see the location of seal 4 inFIG. 2). The glass with frit on it may optionally be heated at thispoint to about 120 degrees C. for about 15 minutes to evaporate thesolvent of the deposited seal material. The second substrate 3 is thenbrought down over the first substrate so as to sandwich the spacers 5and seal material 12 therebetween (step 29), with a pressure of e.g.,about 0.15 psi all around or everywhere. Optionally, the unit includingthe substrates 2, 3, spacers 5, and edge seal material 12 may bepre-heated to a temperature of from about 100-250° C., more preferablyabout 200° C. for about 60 minutes, in order to prevent thermal shock inthe glass during the subsequent microwaving step (step 31). Also, step31 may function to help the seal material fuse with the glass substratesby heating the substrates, and/or may enable binder to burn off forhermeticity purposes. Optionally, the oven temperature may be raised toabout 430 degrees C. at this point, letting the stack remain at thattemperature for about 60 minutes. The edge seal material 12 may beheated via microwave energy as discussed above in order to form hermeticperipheral/edge seal 11 (step 33). The oven cooling rate may then be setto about 2.8 degrees C. per minute to allow the stack to cool, whilelowering the oven temperature to about 310 degrees C. and letting it atthat temperature for about 30 minutes during the cooling process. Thestack may then be permitted to cool at room temperature at its own rate,roughly 2 degrees C. per minute. Thereafter, a vacuum is drawn (e.g.,via a pump out tube located at any suitable position on the unit) inorder to form low pressure space or cavity 6 between the substrates(step 35).

[0069]FIG. 8 is a cross sectional view illustrating that a solder glassseal 41 around a hollow pump-out tube 43 may also be formed usingmicrowave energy 17 from a microwave generator 15 as described above.This embodiment is the same as the embodiment of FIGS. 1-7, except thatthe seal material heated with the microwave energy is a seal materialprovided around at least a portion of a pump-out tube 43. Afterformation of the hermetic seal 41, the central cavity between the glasssubstrates 2, 3 may be evacuated by drawing a vacuum out of the cavityvia tube 43 as shown in FIG. 8 so as to create low pressure space 6. Theformation of a pump-out tube seal 41 using microwave energy may be doneeither in combination with or separately from formation of an edge sealusing microwave energy in different embodiments of this invention.

[0070]FIG. 9 is a flowchart illustrating steps that may be takenaccording to yet another embodiment of this invention. The FIG. 9embodiment is similar to the FIG. 7 embodiment, with a few notableexceptions. For example, substrate(s) 2, 3 are originally provided inthe FIG. 9 embodiment with a low-E coating thereon (step 51). The edgeseal material 12 is then deposited around an edge portion of one of thesubstrates prior to tempering (step 53). Thereafter, one or both of thesubstrates is/are tempered along with the edge seal material thereon(step 55). During the tempering step, the edge seal material is causedto fuse with the glass substrate upon which it is provided. Then,spacers 5 are deposited on one of the substrates 2, 3 (step 57). The twosubstrates 2, 3 are brought together with spacers 5 therebetween (step59). Unlike the FIG. 7 embodiment, at this point the edge seal materialmay be in a hardened state. Thereafter, microwave energy described aboveis used to heat the edge seal material in order to melt at least aportion of the same in order to for the hermetic edge seal (step 61). Asmentioned above, a hermetic seal around the pump-out tube may optionallybe formed using microwave energy as well. Thereafter, a the spacebetween the substrates 2, 3 is evacuated so as to form low pressurespace 6 (step 63).

[0071] FIGS. 10-11 illustrate another embodiment of this invention.According to the FIGS. 10-11 embodiment, edge seal material is depositedaround the entire periphery of one (or preferably both) of annealedglass substrates 2 and 3 prior to thermal tempering of the substrates.Then, the substrates 2, 3 with edge seal material thereon are thermallytempered. Following tempering, the substrates are brought together so asto sandwich spacers therebetween and microwave energy is used asdescribed above in order to heat the edge seal material on one or bothsubstrates thereby causing the edge seal material to fuse together so asto form the hermetic edge seal of the vacuum IG unit. This embodimentmay be considered as an improvement over the FIGS. 5-8 embodiments ofthis invention because diffusion of the edge seal material into atempered glass substrate is more difficult than diffusion of the edgeseal material into an annealed non-tempered glass substrate. Thus, byheating the edge seal material and causing it to diffuse into thesubstrates during the thermal tempering process, improved bonding of theedge seal material to the respective substrates may be achieved. Thelikelihood of glass cracking may also be reduced in accordance with thisembodiment.

[0072] Referring more specifically to FIGS. 10-11, a more detaileddescription of this embodiment follows. Initially, first and secondannealed non-tempered glass substrates 2, 3 are provided. Optionally, alow-E coating or coating system 14 may be provided on at least one ofthe substrates 2, 3. Edge seal material 12 (e.g., glass frit suspendedin liquid or solvent) is deposited around an edge or periphery of amajor surface of at least the first substrate 2 and preferably also thesecond substrate 3 (see FIG. 10(a), and step 91 in FIG. 11; also, seethe location of seal 4 in FIG. 2). Seal material may either be depositeddirectly on a surface of a substrate 2, 3, or alternatively but notpreferably may be deposited on the substrate 2, 3 with another layer(s)therebetween. Then, the glass substrate(s) 2, 3 with edge seal material12 thereon are thermally tempered so as to diffuse the seal material 12into the respective glass substrates thereby forming hardened sealportions 12 a as shown in FIG. 10(b) (step 93 in FIG. 11). This thermaltempering, in certain exemplary embodiments, may be conducted at atemperature of from about 600-700 degrees C. Thus, the heat utilizedduring the thermal tempering process both tempers the glass substrates 2and 3, and also causes the seal material 12 to diffuse into therespective substrates to form cured solder glass seal portions 12 a. Thesubstrates are permitted to cool in accordance with conventionaltempering techniques. Then, second substrate 3 with seal portion 12 athereon is then brought down over the first substrate 2 with sealportion 12 a thereon so as to sandwich the spacers 5 and seal materialportions 12 a therebetween (see FIG. 10(b), and step 95 in FIG. 11).Optionally, the unit including the substrates 2, 3, spacers 5, and edgeseal material 12 may be pre-heated at this point to a temperature offrom about 100-250° C., more preferably about 200° C. for about 60minutes, in order to prevent thermal shock in the glass during thesubsequent microwaving step (step 97). The edge seal portion(s) 12 a maythen be re-heated via microwave energy as discussed above in order tore-melt the edge seal material thereby forming hermetic peripheral/edgeseal 11 as shown in FIG. 10(c) (step 99). This embodiment may requiremore microwave energy than the previous embodiment due to the need forre-melting of the edge seal material. The stack may then be permitted tocool. Thereafter, a vacuum is drawn (e.g., via a pump out tube locatedat any suitable position on the unit) in order to form low pressurespace or cavity 6 between the substrates (step 101).

[0073] FIGS. 12-13 illustrate another embodiment of this invention. Thisembodiment differs from previous embodiments in that first and seconddifferent applications of glass frit in solution are utilized during themanufacturing process. The first frit application (of a first viscosity)is applied prior to thermal tempering of the substrates. This glass fritis bonded to or fused into the glass (one or both of the substrates)either during the thermal tempering process or prior thereto during aseparate heating step. The second frit application (of a secondviscosity) is applied after tempering over the first frit application onat least one of the two substrates. The two frit applications may be ofapproximately the same viscosity in certain embodiments, and in otherembodiments the second application is of a higher viscosity than thefirst application so that the second application is more paste-like.After the two substrates are brought together so as to sandwich thespacers 5 therebetween, the second frit application is heated (e.g., viamicrowave energy, or any other suitable energy) when it is in contactwith the first frit from both substrates, thereby causing the secondfrit application to bond or adhere to the first frit applications. Aftercuring, the hermetic edge seal 11 results.

[0074] Referring more particularly to FIGS. 12 and 13, two float glasssubstrates 2 and 3 are provided (with or without low-E coating(s)thereon) (step 201). A first application of glass frit in solution 301(e.g., Ferro 4000 frit in solution, where the solution is typically usedfor automotive windshield black-border applications and is obtainablefrom O. Hommel Co., Carnegie, Pa. (the black pigment and glass frit maybe deleted from this with Ferro 4000 then added to it)) is applied to amajor surface of each of the two substrates proximate an edge portionthereof as shown in FIG. 13(a) (step 203). This first application 301 ofglass frit material constitutes an edge seal base material, and may belocated in the same location as the edge seal in FIG. 2 or anywhere elseproximate the peripheral edge of the substrate(s). First application 301of frit in solution may be from about 0.01 mm to 0.10 mm thick on eachof the two substrates 2, 3 in certain exemplary embodiments of thisinvention. A preferred thickness is from about 0.03 mm to 0.08 mm. Thesefrit 301 painted substrates may then be dried in an oven (e.g., at fromabout 80-200 degrees C., more preferably at about 120 degrees C.) for aperiod of from about 1 to 5 hours (e.g., preferably about 2.5 hours).Thus, in certain embodiments, the frit 301 may be fused or bonded to theunderlying substrate(s) in a separate heating step before the temperingprocess begins (however, this bonding may also be done primarily duringthe tempering heating process in other embodiments).

[0075] The frit 301 painted substrates of FIG. 13(a) are then thermallytempered in a known manner (e.g., using temperatures of from about600-700, or 600-800, degrees C.) as discussed above (step 205). Duringtempering (and/or prior thereto as discussed above), the frit 301 fusesinto and/or bonds with the underlying substrate(s) 2, 3. The temperedsubstrates with solder glass/glass frit 301 thereon may optionally becleaned using hot water and/or soap, and/or then rinsed with distilledwater. The tempered substrates with frit layer 301 thereon may thenoptionally be dehydrated (e.g., on a 120 degree C. plate for fiveminutes).

[0076] Following tempering, FIG. 13(b) illustrates that the second glassfrit application 303 is applied at least partially over the cured firstglass frit or solder glass 301 on at least one of the substrates (step207). In FIG. 13(b), the second glass frit in solution application 303is only provided over solder glass 301 on one of the two substrates,although it may be applied in a similar manner on both substrates inalternative embodiments of this invention. For the second application,Ferro 4000 may be in F-1016AJ solution obtained from Pierce & Sevens,Buffalo, N.Y. As applied, the second glass frit 303 has a higherviscosity than the first glass frit 301 in certain embodiments of thisinvention (this has been found to help limit flow of the secondapplication 303 thereby enabling easier alignment of the two portions301 during the later sandwiching step. This second glass frit layer 303application may then optionally be dried (e.g., on a 120 degree C. hotplate for five minutes). Spacers 5 are deposited on a substrate 2, 3having both frit applications thereon (step 209).

[0077]FIG. 13(c) illustrates that the two substrates 2, 3 are thenbrought together so as to sandwich spacers 5 and the two glass fritapplications/layers therebetween (step 211). During this step, thesecond glass frit layer 303 ends up being in contact with layer 301 ofon each substrate 2, 3 as shown in FIG. 13(c). Optionally, the unit maythen be preheated to a temperature of at least about 200 degrees C.,more preferably of at least about 300 degrees C., and even to atemperature of about 380 degrees C. (step 213). Microwave energy 17 fromat least one source 15 as described above in other embodiments of thisinvention is then used to heat at least the edge seal area (and thusfrit layers 301 and 303) thereby melting the frit of 303 and causing itto fuse into and/or bond with pre-fired frit or solder glass 301 (step215). This microwave energy may be used to heat the material 303 to atemperature of at least about 350 degrees C., more preferably to atemperature of at least about 400 degrees C., and most preferably to atemperature of from about 400 to 500 degrees C. for a period of time offrom about 0.05 to 15.0 minutes. This heating causes the frit/glasslayer 303 to bond with frit/glass layers 301. After cooling (in ambientconditions or otherwise) down (e.g., to room temperature), the hermeticedge seal 11 has been formed. The space/gap between the substrates isthen evacuated to create low pressure space 6 (step 217).

[0078] Regarding then FIGS. 12-13 embodiment, it has surprisingly beenfound that this technique results in a significantly stronger vacuum IGunit than has been previously achievable with standard solder glass edgeseals shown in FIGS. 1-2 above. For example, a conventional design witha solder glass edge seal like that of FIGS. 1-2 experienced wedge test(pushing a wedge between the substrates) failure at 1.99 lbf (poundsforce) and a sheer failure at 190 lbf. In contrast, an example of theembodiment of FIGS. 12-13 did not experience wedge test failure until3.75 lbf (cohesive failure) and sheer failure at 225.8 lbf. Thus, it canbe seen that the maximum load is distributed much more uniformly in theFIGS. 12-13 embodiment than in FIG. 6(c). The FIGS. 12-13 embodiment isstronger than the FIGS. 1-2 embodiment (with approximately the sameuniformity however). Accordingly, this embodiment of this inventionprovides a better uniformity in the final hermetic edge seal 11.

[0079] It is also noted that an example of the FIG. 6 embodiment of thisinvention experienced wedge test failure at 2.5 lbf and shear failure at171.5 lbf. Thus, it can be seen that the FIG. 6 embodiment of thisinvention surprisingly results in a stronger and better overall edgeseal than the prior art of FIGS. 1-2, but not quite as good as the FIGS.12-13 embodiment of this invention.

[0080] Once given the above disclosure, many other features,modifications, and improvements will become apparent to the skilledartisan. Such other features, modifications, and improvements aretherefore considered to be a part of this invention, the scope of whichis to be determined by the following claims.

What is claimed is:
 1. A method of making a thermally insulating glasspanel, the method comprising: depositing a first portion of edge sealmaterial on first and second glass substrates; thermally tempering thefirst and second glass substrates with the first portion of edge sealmaterial thereon; following said tempering, depositing a second portionof edge seal material on at least the first substrate over at least partof the first portion of edge seal material already on the firstsubstrate; forming a hermetic peripheral or edge seal at least partiallybetween the first and second substrates by at least using microwaveenergy directed toward at least the second portion of edge seal materialso that the second portion of edge seal material bonds to both: a) thefirst portion of edge seal material on the first substrate, and b) thefirst portion of edge seal material on the second substrate; andevacuating a space between the first and second substrates so as to forma low pressure area having a pressure less than atmospheric pressurebetween the first and second substrates.
 2. The method of claim 1,wherein said forming a hermetic peripheral or edge seal using at leastmicrowave energy is carried out in a manner so that after the hermeticedge seal has been formed at least certain portions of the first andsecond substrates retain at least about 50% of their original temperstrength.
 3. The method of claim 2, wherein at least certain portions ofthe first and second substrates retain at least about 70% of theiroriginal temper strength after the hermetic edge seal has been formed.4. The method of claim 3, wherein at least certain portions of the firstand second substrates retain at least about 80% of their original temperstrength after the hermetic edge seal has been formed, and wherein themethod further comprises heating the first portion of edge seal materialprior to said tempering in order to cause the first portion of edge sealmaterial to bond to said substrates prior to said tempering.
 5. Themethod of claim 1, wherein said forming a hermetic peripheral or edgeseal at least partially between the first and second substrates usingmicrowave energy comprises directing microwave energy having awavelength of from about 1-10 mm toward an edge seal material in orderto form the hermetic edge seal.
 6. The method of claim 5, wherein saidforming a hermetic peripheral or edge seal at least partially betweenthe first and second substrates using microwave energy comprisesdirecting microwave energy having a wavelength of from about 2-8 mmtoward the edge seal material in order to form the hermetic edge seal.7. The method of claim 1, wherein said tempering comprises heating saidglass substrates with the first portion of edge seal material thereon toa temperature of from about 600-700 degrees C. so that at least aportion of edge seal material is at least partially diffused into one ofthe substrates during the tempering.
 8. The method of claim 1, whereinsaid forming a hermetic peripheral or edge seal at least partiallybetween the first and second substrates using microwave energy comprisesdirecting microwave energy in the form of a beam toward an edge orperipheral portion of at least one of the substrates to the exclusion ofat least a central portion of said at least one substrate in order toform the hermetic edge seal.
 9. The method of claim 8, wherein the edgeseal is of a material more absorptive to certain wavelengths ofmicrowave energy than is glass of the substrates.
 10. The method ofclaim 1, further comprising providing a plurality of spacers between thefirst and second substrates, and wherein said first portion of edge sealmaterial comprises solder glass or glass frit.
 11. The method of claim10, further comprising providing a low-E coating or coating system on atleast a portion of an interior major surface of at least one of thefirst and second substrates.
 12. A method of making a seal of athermally insulating glass panel, the method comprising: thermallytempering a glass substrate with edge seal material thereon; providingadditional edge seal material on said substrate following saidtempering, so that the additional edge seal material contacts the edgeseal material provided or deposited on the glass substrate prior to saidtempering; providing a plurality of spacers between the tempered glasssubstrate and another glass substrate; and forming a seal located atleast partially between the substrates by heating at least theadditional edge seal material so that the additional edge seal materialfuses with or bonds to the edge seal material deposited on the glasssubstrate prior to said tempering.
 13. The method of claim 12, whereinthe seal is a solder glass inclusive seal, and where the method furthercomprises: evacuating a space between the substrates so as to form avacuum or low pressure area having a pressure less than atmosphericpressure between the substrates; and wherein said heating comprisesusing microwave energy to heat both the additional edge seal materialand the edge seal material deposited on the glass substrate prior tosaid tempering so that the additional edge seal material fuses with orbonds to the edge seal material deposited on the glass substrate priorto said tempering.
 14. The method of claim 12, wherein at least certainportions of the glass substrate retains at least about 70% of itsoriginal temper strength after the seal has been formed; and wherein theedge seal material provided on the glass substrate during said temperingfuses into or with the glass substrate during at least one of: (a) saidtempering, or (b) during a separate heating step carried out prior tosaid tempering.
 15. A method of making a seal, the method comprising: atleast partially tempering a first substrate with a first application ofseal material thereon; and following said tempering, adding a secondapplication of seal material and using microwave energy to heat thefirst and second applications of seal material in order to form a sealat least partially located between the first substrate and a secondsubstrate.
 16. The method of claim 15, further comprising: providing aplurality of spacers between the substrates; wherein the seal is ahermetic edge seal; and evacuating a space between the first and secondsubstrates so as to form a vacuum or low pressure area having a pressureless than atmospheric pressure between the first and second substrates.17. A thermally insulating glass unit comprising: first and second atleast partially tempered glass substrates spaced apart from one anothervia at least a plurality of spacers; a microwave energy-formed hermeticperipheral or edge seal located at least partially between the first andsecond substrates, at least a portion of material for said peripheral oredge seal having been deposited on at least one of the substrates priorto tempering of the at least one substrate; said peripheral or edge sealhaving been formed in a manner such that at least certain portions ofthe at least one substrate retain at least about 50% of original temperstrength after microwave formation of the peripheral or edge seal; and aspace having a pressure less than atmospheric pressure provided betweensaid substrates and sealed off by said microwave energy-formed hermeticperipheral or edge seal.
 18. The unit of claim 17, wherein saidmicrowave energy-formed hermetic peripheral or edge seal comprises asolder glass inclusive peripheral or edge seal.
 19. A method of making aseal for a thermally insulated panel, the method comprising: heating afirst substrate with base seal material thereon to a temperature of fromabout 600-700 degrees C.; and following said heating, applyingadditional seal material and using microwave energy to re-heat the baseseal material and heat the additional seal material in order to form aseal at least partially located between the first substrate and a secondsubstrate.
 20. The method of claim 19, wherein the base seal materialand the additional seal material both comprise solder glass or glassfrit, and the first and second substrates are glass substrates.
 21. Amethod of making a thermally insulating unit, the method comprising:providing first and second substrates with a plurality of spacerstherebetween; and forming a hermetic peripheral or edge seal at leastpartially between the first and second substrates using at leastmicrowave energy.
 22. The method of claim 21, further comprisingevacuating a space between the first and second substrates.
 23. Athermally insulating panel comprising: first and second spaced apartsubstrates having a low pressure space therebetween having a pressureless than atmospheric pressure; a hermetic seal provided between saidfirst and second substrates; and wherein said seal includes first andsecond solder glass or glass frit seal portions, at least a portion ofsaid first seal portion having been deposited on said first substrateprior to tempering thereof and said second seal portion having beendeposited on one of said substrates following tempering thereof.
 24. Thethermally insulating panel of claim 23, wherein said seal comprises aperipheral or edge seal, and wherein said seal is formed via at leastmicrowave heating.
 25. The thermally insulating panel of claim 23,further comprising a plurality of spacers provided between thesubstrates.
 26. A method of making a seal of a thermally insulatingglass panel, the method comprising: heating a glass substrate with edgeseal material thereon; providing additional edge seal material on saidsubstrate following said heating, so that the additional edge sealmaterial contacts the edge seal material provided or deposited on theglass substrate prior to said heating; providing a plurality of spacersbetween the glass substrate and another glass substrate; and forming aseal located at least partially between the substrates by performinganother heating in order to heat at least the additional edge sealmaterial so that the additional edge seal material fuses with or bondsto the edge seal material deposited on the glass substrate prior to saidprevious heating.